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Nano-coating To Make Implants MRI Safe
Makarand writes "Patients who have implants containing any kind of metal cannot be MRI scanned as the powerful electromagnetic radio
waves can induce currents large enough to heat the metal in implants to over 70 C and damage surrounding tissue.
Now, Biophan, a biomedical devices company, has
developed a nano-coating material that can protect implants by preventing most of the radio waves
from reaching the internal components of the implant by reflecting them. It's high electrical
resistance also prevents currents from flowing around the implant's surface and heating
any nearby body tissue.
Biophan's coating is a mixture of poorly conducting nanoparticles
held in an insulating matrix. The coating is a mere three micrometres thick
and can cut the energy induced in an implant by 89 per cent."
I was an MRI tech for 4 years, so golly I have special experience here. Our primary reason for restricting metal was not heating -- the RF is not all that strong, not like a microwave -- but the 1.5 Tesla magnetic field (that's a moderately strong magnet). Our concern was that the field would pull or twist something sensitive like an aneurysm clip. Also the metal would cause a distortion in the magnetic field such that it was impossible to extract images near something fixed, such as screwed into bone -- the biggest practical problem here.
:), which would be susceptible to induced current. We were mostly worried about older pacemakers that were not entirely solid-state. Many pacemakers are not full-time, btw, that it the heart can work without them.
The field is *powerful* -- in one case it took several of us to pull free a chunk of metal another tech had unwittingly brought into the room.
I can see how this would be useful for non-magnetic materials like most stainless (yes, there are magnetic blends of ss in the 4xx series before someone tries to correct me
(Rudimentary MRI primer: the primary field sets up a net alignment of molecules in the body, most significantly water; the RF pulses then tweak these molecules so they emit RF of their own, revealing location and quantity. Things have evolved since i was a tech, however.)
I think you missed the part about "conductive nanoparticles that are implanted in the non-conducting matrix". As you might know from transformator theory, you can reduce eddy current loss in the yoke by making the yoke from a stack of thin metal sheets rather than a solid yoke, i.e. reducing the size of continuous metal parts.
They said *electrical* insulator. So they aren't supposed to stop radiating fields, that's what the metal/semiconductor particles are for. The insulator is supposed to stop heat/current from building up by preventing a current from ever flowing through/around the device.
So what they are describing is a very poor Faraday cage embedded inside a non conducting matrix.
Like rebar inside a concrete building!
Notice how you get no cell phone reception inside? The building is acting like a Faraday cage by reflecting and absorbing all the radio.
If you use a copper sheath, for example, you have an *excellent* conductor; it means it will absorb the RF, convert it into electricity, and then that electricity, being essentially an inductive short, will heat up as more energy is pumped into it, and then get dumped back into the body as heat.
GPL Deconstructed
Many, but far from all, metals are ferromagnetic. Amalgams (compounds with mercury) in dental fillings are generally diamagnetic.
A given metal atom may pair up its electrons and become diamagnetic if its local chemical enviroment encourages it even if in bulk the metal is ferromagnetic. (Yes, there are iron compounds which are not ferromagnetic)
There also exist unpaired electrons in organic compounds, but they're generally not very stable. ('Free Radicals')
It would have no effect on metal detectors. The metal detectors work by sensing the rather distinct change in magnetic permeability of the space near the coil that occurs when something containing ferromagnetic elements (iron, nickel, cobalt) is present.
By the way, did anyone else think that guy mentioned in the article who died because he failed to mention his pacemaker (even when asked several times) should be nominated for a Darwin award?
Believe me, anyone who works with MRI is aware of the risk! We wouldn't even keep things in our pockets, including easily erased bank cards!
.. I once scanned a prisoner in full shackles because the two rather large police escorts said he was too dangerous to remove them ... but they were attached, hence not a problem). Perhaps a piece of equipment is inadvertantly presumed safe, as by my very diligent coworker who took in an IV pole that looked just like ours (there are expensive aluminum equivalents to these items) -- the pole was aluminum, but not the base. Perhaps a walk-in patient doesn't tell when interviewed about the Zippo lighter in her pocket which then almost smacks into the tech's (my) head.
But accidents happen. Perhaps you have someone unfamiliar visiting like that cop (I bet he just walked into the room before they had a chance to demetal him
The room seems no different from anywhere else, and the magnetic field increase exponentially as you approach, easily ripping something away before you can react.
A prudent solution is an airport-style metal detector. There are practical problems with using them that i don't recall; some places do use them. The wands work, but leave you vulnerable to the vacant-brain syndromes above.
As for the Westchester oxygen bottle, I believe what happened was that a magnetic-safe gurney was used but the ordinary oxygen bottle was concealed n the tray beneath by the sheet. This does not justify the tragedy, but demystifies it some. We always followed accidents with great interest.